1. Field of the Invention
The present invention relates to a method of producing a toothed belt of plastics material or similar extrudable material, with a reinforcing insert in the form of wire or thread extending in the longitudinal direction of the belt, and with a fabric cover which covers the toothed side of the belt; a mold cavity is formed between a molding wheel which can be driven continuously and which is provided on its periphery with an annular depression which is profiled in the manner of a gear wheel and and which corresponds in cross section to the cross section of the belt which is to be produced, and a cover which closes the depression over a portion of the periphery of the molding wheel; and the plasticized plastics material is introduced into the beginning of the mold cavity through a nozzle which can be used for the sealed introduction of the reinforcing insert and/or the fabric cover.
2. Description of the Prior Art
According to German Pat. No. 28 01 604, and corresponding U.S. Pat. No. 4,251,306--Breher dated Feb. 17, 1981 liquid plastics material and a strip of fabric are introduced into the mold cavity in order to obtain a finite strand of toothed belt which is covered with the strip of fabric on its toothed side, from which strand a wide piece of flexible tube is subsequently formed by winding and embedding a subsequently applied reinforcing insert, from which piece of flexible tube endless toothed belts of any belt width can be cut off.
According to German Pat. No. 21 23 902, and corresponding U.S. Pat. Nos. 3,880,558--Breher et al. dated Apr. 29, 1975 and 3,999,914--Breher et al. dated Dec. 26, 1976 as a divisional thereof liquid plastics material and a reinforcing insert are introduced into the mold cavity in order to obtain a reinforced finite strand of toothed belt which can be closed to form an endless reinforced toothed belt of any length of belt circumference by suitable connection of the ends of the belt strand. In principle, it is possible to also introduce a strip of fabric into the mold cavity in order to obtain a reinforced finite strand of toothed belt which is covered on its toothed side with the strip of fabric.
During the production of both of the aforementioned known toothed belts, the strip of fabric must be resiliently extensible in its longitudinal direction in order that the strip of fabric in the mold cavity, where it at first covers the grooves between the teeth in the molding wheel depression in a hollow manner, can be pressed into the grooves between the teeth in the molding wheel depression by the plastics material, which is introduced under pressure. During the introduction of the strip of fabric into the mold cavity, the problem has arisen that the soft and stretchably extensible fabric cannot be guided satisfactorily laterally, so as to run straight and flat into the mold cavity. There is the risk that the strip of fabric may shift sideways, may compress at one side of the mold cavity, or may fold over, so that no toothed belt satisfactorily covered with fabric on its toothed side is produced.
It is an object of the present invention to provide a method of the aforementioned general type which overcomes the described problems.